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From James Taylor <jamestay...@apache.org>
Subject Re: Disabling HBase Block Cache
Date Fri, 25 Mar 2016 17:27:45 GMT
Hi Amit,

Have you see our documentation and examples for ALTER TABLE [1]?

So you could do ALTER TABLE my_table SET BLOCKCACHE=false;

If you want to prevent rows from being put in the block cache on a per
query basis, you can use the /*+ NO_CACHE */ hint [2] on a query like this:

SELECT /*+ NO_CACHE */ ...

Thanks,
James

[1] https://phoenix.apache.org/language/index.html#alter
[2] https://phoenix.apache.org/language/index.html#hint

On Fri, Mar 25, 2016 at 6:39 AM, Amit Shah <amits.84@gmail.com> wrote:

> I noticed that the charts <http://i.imgur.com/ZEJTHWt.png>on cloudera
> indicate no block usage when the group by query is executed. This probably
> means that the block cache is disabled. The only strange fact is that the
> hbase shell describe command gave BLOCKCACHE => 'true'. It would be great
> if someone could throw some light on this.
>
> P.S - Though disabling the block cache didn't speed up the group by query
> but that seems like a separate topic of discussion.
>
> Thanks!
>
> On Fri, Mar 25, 2016 at 1:34 PM, Amit Shah <amits.84@gmail.com> wrote:
>
>> Hi,
>>
>> I am using apache hbase (version 1.0.0) and phoenix (version 4.6)
>> deployed through cloudera. Since my aggregations with group by query is
>> slow, I want to try out disabling the block cache for a particular hbase
>> table. I tried a couple of approaches but couldn't succeed. I am verifying
>> if the block cache is enabled/disabled through the hbase shell - describe
>> 'my_table' command.
>>
>> 1. Set 'hfile.block.cache.size' property from cloudera console to 0
>>
>> 2. alter 'myTable', CONFIGURATION => {NAME => 'myColumnFamily',
>> BLOCKCACHE => 'false'}
>>
>> Even after the above two steps, I get BLOCKCACHE => 'true' in the
>> describe command output
>>
>> COLUMN FAMILIES DESCRIPTION {NAME => '0', DATA_BLOCK_ENCODING =>
>> 'FAST_DIFF', BLOOMFILTER => 'ROW', REPLICATION_SCOPE => '0', COMPRESSION =>
>> 'NONE', VERSIONS => '1', MIN_VERSIONS => '0', TTL => 'FOREVER',
>> KEEP_DELETED_CELLS => 'FALSE', BLOCKSIZE => '65536', IN_MEMORY => 'false',
>> BLOCKCACHE => 'true'}
>>
>> What could be going wrong? Any suggestions?
>>
>> Thank you.
>>
>>
>>
>

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